1. Field of the Invention
The present invention relates to a device for varying a timing and lift of a valve in a reciprocating-type internal combustion engine.
2. Description of the Prior Art
Engine speeds of an internal combustion engine usually vary from about 500 rpm to 6,000 rpm and air volumes taken into the combustion chamber widely vary. In a reciprocating-type internal combustion engine, in which the air volumes taken into the combustion chamber and exhausted from the combustion chamber are controlled by the opening and closing of the intake valve and the exhaust valve respectively, it is necessary to open the intake valve for a longer time in order to take more air into the combustion chamber. Thus, to obtain a high output in a region of high speeds, this valve must be opened for a long time. However, when the intake valve is opened for a long time, the open periods of the intake valve and the exhaust valve increasingly overlap each other and the exhaust gas increasingly exits to the intake port, especially in a range of low speeds, thereby reducing the engine output.
Generally, in a range of low speeds, particularly in a range near idling, the open periods of the intake valve. In fact, the exhaust valve are not required to be long and long open periods of the valves will destabilize the engine speed. In order to optimize the air intake and exhaust timings, it is necessary to control the valve timing and lift with respect to engine operating conditions which vary from moment to moment. This is the reason why a device for varying a valve timing and lift is required.
In a gasoline engine, unlike a diesel engine, a throttle valve is provided in the intake path, and the engine may operate at partial capacity by throttling the air supply with the throttle valve. Since there is an intake pressure loss due to throttling, the fuel efficiency of the gasoline engine is not as high as that of a diesel engine. However, if the throttle function is performed by the intake valve in the gasoline engine, that is, if the lift of the intake valve is controlled corresponding to engine loads and the throttle pressure loss at the throttle valve is eliminated, fuel efficiency and engine output will be improved to a great extent. This is another reason why a device for varying a valve timing and lift for an internal combustion engine is required.
In order to satisfy the above requirements, various devices for varying a valve timing and lift have been proposed. Also, similar techniques to make the intake valve operable or not operable, thereby changing the number of the operating cylinders, have been proposed. For example, Japanese Utility Model Publication No. SHO 55-152307 discloses that the tappet length should be changed between high speeds and low speeds, thereby changing the valve timing. Japanese Utility Model Publication No. SHO 58-122713 teaches supplying either only oil to the oil pressure chamber of the tappet or both oil and air to the oil pressure chamber to vary the valve lift. Japanese Utility Model Publication No. SHO 58-130005, Japanese Utility Model Publication No. SHO 58-130006 and Japanese Utility Model Publication No. SHO 58-130045 disclose diverting a portion of the oil to the oil pan without being supplied to the oil pressure chamber by means of a solenoid valve, thereby changing the valve timing. In addition, Japanese Patent Publication No. SHO 55-109711 and Japanese Patent Publication No. SHO 54-57009 provide similar teachings.
However, any one of the above publications discloses no more than a binary change in valve timing and lift from one state at low speeds to another state at high speeds. The prior art did not control valve timing and lift continuously, corresponding to the continuous range of intermediate engine speeds and loads. Thus, a finer control of the valve timing and lift has been demanded to improve the engine performance, specifically the output and the fuel efficiency of the engine.